There are a wide variety of applications in which it is desirable or necessary to separate a floating substance from a liquid. The floating substance may, for example, be another liquid having a lower density. The floating substance may be an unwanted contaminant, or a useful material to be separated from the liquid beneath for use in some application.
Skimmers are a type of separation apparatus widely used in industry to remove floating contaminants, such as oil, from the surface of water or another liquid, such as an aqueous cleaning or coolant solution. Known skimmers typically consist of a pick up, a pump, and a unit in which coalescence or filtration, and then settlement, takes place. This is typically carried out in a small tank or in a small drum modified for the purpose. A typical coalescence unit, as used in prior art skimmers, is shown highly schematically in FIG. 1. A supply of dirty coolant (i.e. containing contaminant oil) is provided to the intake, which directs this supply downwards into a coalescing cartridge contained in a drum. This cartridge extracts the contaminant oil, and relatively clean coolant is extracted via an outlet fed from the bottom of the drum. A problem with such skimmers is that, as they rely on coalescence techniques to improve separation of the oil and water, they can block with fine solids and require changing or cleaning. The time between cleaning or changing is difficult to gauge.
Known alternatives to skimmers using coalescence techniques are units that rely on hydrophobic ropes, belts or discs. Generally, however, these units are hard to maintain and do not work successfully over a prolonged period.
Another known form of separation apparatus is shown in FIG. 2. A supply comprising oil, water, and solids is supplied via an inlet into a separation chamber, to emerge within the body of water already collected in the chamber. Oil rises to the surface, and is tapped off via an outlet, and solids accumulate at the bottom of the chamber. Water is extracted from the side of the chamber. A problem with such an arrangement is that injection of the supply causes churning which impedes the separation process. This is a particular problem if the supply also comprises a large amount of entrained air. Therefore, in the past, there has been motivation to keep the amount of entrained air in the supply to a minimum.
It is therefore an object of embodiments of the present invention to provide separation apparatus and techniques which overcome, at least partially, one or more of the problems associated with the prior art. Particular embodiments aim to provide improved skimming apparatus.